Neuromuscular Blocking and Vagolytic Effects of Atracurium, Cisatracurium, and Mivacurium in the Anesthetized Cat / 대한마취과학회지

BACKGROUND: Atracurium is a benzylisoquinolium nondepolarizing neuromuscular blocking drug. It releases histamine upon the rapid administration of more than 2 x ED95. Cisatracurium is about three to four times more potent than atracurium, less likely to release histamine, and has weaker cardiovascular or autonomic effects. Mivacurium releases histamine to about the same degree as atracurium at the same dose. This study was undertaken to reevaluate the experimental model for the evaluation of effects on the autonomic nervous system, and to determine the neuromuscular blocking profiles and the vagolytic effects of atracurium, cisatracurium and mivacurium in cats. METHODS: Cats, either sex, anesthetized with pentobarbital, were used. Neuromuscular blocking effects were assessed using the effects on the anterior tibialis muscle twitch evoked with supramaximal stimuli (0.2 ms-duration, 0.1 Hz). Inhibition of the parasympathetic nervous system was assessed in response to bradycardia to vagal nerve stimulation with ten-second trains of square-waves (0.5 ms-duration, 20 Hz). The dose-response curves for both neuromuscular blocking and vagolytic actions were determined for each animal. The dose-response curves were constructed in cumulative fashion. The response for vagal stimuli was measured two minute after each dosing. Vagal ID50 (The doses that produced 50% inhibition of the response to vagus nerve stimulation) were determined. RESULTS: NMB ED95 and NMB ED50, respectively, were 102.0 +/- 28.3 and 143.7 +/- 40.5 microgram/kg for atracurium, 81.4 +/- 13.3 and 110.7 +/- 18.8 microgram/kg for cisatracurium, and 56.8 +/- 17.4 and 74.2 +/- 25.0 microgram/kg for mivacurium. Vagal ID50 was 2,654 +/- 1,651 microgram/kg for atracurium, 655 +/- 389 microgram/kg for cisatracurium, and 606 +/- 182 microgram/kg for mivacurium. The vagal ID50/NMB ED95 and vagal ID50/NMB ED50 were 18.5 and 26.0 for atracurium, 5.9 and 8.1 for cisatracurium, and 8.2 and 10.7 for mivacurium. CONCLUSIONS: Atracurium has a wider margin of safety only for vagal stimulation as compared with cisatracurium and mivacurium. However, we couldn't exclude that either sympathetic stimulation or histamine release might contribute to heart rate.

Age-related Difference of the Vagal Reflex and Baroreceptor Reflex under General Anesthesia with Enflurane / 대한마취과학회지

BACKGROUND: Baroreceptor reflex responds to the decrease in blood pressure caused by drug, dehydration, or severe bleeding. Vagal reflex caused by direct pressure on vagus nerve, the traction, or lung inflation develops bradycardia and severe arrhythmia. Lung inflation elicits a vasodepressor reflex, resulting in stimulation of the vagus nerve which causes a decrease in sympathetic outflow. METHODS: 75 patients who had elective surgery were divided into 3 groups according to the age, such as group I: or = 65 years of age. Lung inflation test has been performed at 20 cmH2O for 20 seconds. Baroreceptor was stimulated by lowering blood pressure with intravenous infusions of nitroglycerin. Baroreceptor sensitivity was assessed by measuring the decrease in blood pressure. Vagal reflex sensitivity was calculated by the subtraction of G2 (baroreceptor reflex sensitivity after introglycerin infusion) from G1 (heart rate response to lung inflation). RESULTS: Baroreceptor reflex induced by hypotension and vagal reflex originated from lung influe-nced the heart rate inversely when lung inflated. Baroreceptor reflex sensitivity was highest in younger patients and lowest in older patients when nitroglycerin infused. Vagal reflex sensitivity was highest in older patients and lowest in younger patients. CONCLUSIONS: Baroreceptor reflex was most sensitive in younger patients, but vagal reflex was moresensitive in older patients.